1. Field of the Invention
This invention relates generally to ground proximity warning systems of the type that monitor various flight parameters and generate a warning upon the occurrence of a hazardous flight condition, as well as to wind shear warning systems that detect the presence of a wind shear condition and generate a warning when a hazardous wind shear condition is detected. More particularly, the present invention relates to a warning system particularly usable during an approach to a landing phase of flight. The system determines the flight path angle of the aircraft during an approach and generates a warning in the event that the flight path angle (negative) is excessive for the altitude at which the aircraft is flying. The warning criteria are modified by a glideslope deviation signal from an ILS receiver and by a wind shear signal from a wind shear detector so that a less steep angle is required for a warning to be generated if the aircraft is below the glideslope or if wind shears are present. In addition, the glideslope warning criteria are altered during the presence of a wind shear so that a smaller deviation below the glideslope is required to generate a warning.
2. Description of the Prior Art
Various prior art warning systems are known. For example, U.S. Pat. Nos. 3,946,358; 3,947,808; 3,947,809; 4,060,793 and 4,215,334 disclose warning systems that generate warnings during an approach phase of flight when the descent rate of the aircraft is excessive for the altitude at which the aircraft is flying. U.S. Pat. No. 3,925,751 disclose systems that monitor the deviation of the aircraft below the glideslope beam and generate a warning if the glideslope deviation is excessive. U.S. Pat. Nos. 4,725,811 and 4,891,642 disclose wind shear warning systems that detect the occurrence of a wind shear condition and generate a warning upon the occurrence of a decreasing performance wind shear that exceeds a predetermined level. All of the above patents are incorporated herein by reference.
While these warning systems provide a warning upon the occurrence of an excessive deviation from normal operational conditions of the parameter they are monitoring, it is possible that a combination of conditions that are not individually sufficient to generate a warning in the prior art systems could be potentially hazardous. For example, a low intensity wind shear of a magnitude that would not be dangerous per se and hence would not normally cause a warning to be generated, could be hazardous if combined with other potentially hazardous conditions. For example, a low intensity wind shear could prove hazardous when combined with an excessively steep descent angle or with a below the glideslope condition, or with a combination thereof.
It has also been found that while systems that warn of an excessive descent rate during an approach to a landing are effective, the vertical speed varies during an approach along a 3.degree. glideslope for different approach speeds and wind conditions. By measuring actual flight path angle, many of these variations may be reduced, particularly at altitudes below 300 feet above the ground.